Volvox forms hypnozygotes with thick, ornamented cell walls that provide protection from stressful environmental conditions.

 

Volvox reproduces asexually through the formation of autocolonies. Special gonidium cells divide to form daughter colonies that are small versions of the parents but with the flagella facing inwards. When the cells have divided into the same number of cells as the parent colony, the hollow colonies invert through a special pore so that the flagella face outwards. The parent colony splits open to release the newly formed autocolonies.

During oogamous sexual reproduction, colonies produce male gametes and release a glycoprotein pheromone to trigger other colonies to sexually produce either a single egg cell or a packet of 16-64 elongate biflagellate sperm. Larger gonidia reproductive cells in the colony posterior give rise to the gametes and daughter colonies. There may be only a few gonidia per colony, or as many as 50.

Most Volvox species are dioceious, although a few are monoecious. The sperm packets are released from the parent colony and make their way into a female colony where they dissociate and fertilize the egg. Unfertilized eggs can still give rise to new colonies. The resulting zygote has thick, spiny protective walls and may be reddish in color. Only a single biflagellate cell survives the meiotic processes and then divides to form a large colony.